JP7203380B2 - Capacitor electrode, manufacturing method thereof, and capacitor - Google Patents

Description

The present invention relates to a capacitor electrode, a method for manufacturing the same, and a capacitor.

Graphene has a theoretical specific surface area of about 2600 m ² /g and is conductive, so it is promising as an electrode material for capacitors. However, if the distance between the graphene sheets is not properly controlled, the flat graphene sheets will overlap each other to a large extent, and the surface area of the graphene cannot be fully utilized.

In Patent Document 1, a plurality of graphene sheet laminates in which two or more graphene sheets are laminated via a first carbon nanotube are electrically and mechanically three-dimensionally connected to each other by a second carbon nanotube. proposed to use a graphene sheet assembly film. Also, it has been proposed to use single-walled carbon nanotubes with a length of 5 to 20 μm as the first and second carbon nanotubes.

International Publication No. 2012/073998 pamphlet

However, when general carbon nanotubes (CNTs) are used, the basal planes of the CNTs interposed between the graphene sheets hinder ion diffusion between the graphene sheets, so the resistance tends to increase at low temperatures.

One aspect of the present invention includes first carbon and second carbon other than the first carbon, wherein the first carbon includes graphene and the second carbon is short carbon fibers having an average length of 10 μm or less. and/or carbon particles having an average diameter of 0.1 μm or less, wherein the graphenes are stacked with the second carbon interposed therebetween.

Another aspect of the present invention relates to a capacitor including the capacitor electrode.

Yet another aspect of the present invention includes the steps of preparing an aqueous dispersion containing graphene oxide, which is the first carbon raw material, and the second carbon, and reducing the graphene oxide in the aqueous dispersion. and the second carbon is short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less.

According to the present invention, graphene can be used to obtain a capacitor electrode that has a high capacity and a low resistance even at a low temperature.

1 is a partially cutaway perspective view of an electric double layer capacitor according to the present invention; FIG. 1 is an electron microscope (TEM) photograph of the xerogel obtained in Example 1. FIG. 2B is an enlarged TEM photograph of a portion of FIG. 2A; 10 is an electron microscope (SEM) photograph of highly crystalline graphene used in Comparative Example 3. FIG.

The capacitor electrode according to the present embodiment includes first carbon and second carbon other than the first carbon, the first carbon includes graphene, and the second carbon includes short carbon fibers having an average length of 10 μm or less and/or average Carbon particles having a diameter of 0.1 μm or less. And graphene is laminated|stacked through 2nd carbon. Therefore, ion diffusibility between graphenes is greatly improved, and a low-resistance capacitor electrode can be obtained. In addition, by interposing the second carbon between the graphenes, overlapping of the graphene sheets is suppressed, and the surface area of the graphene can be utilized more effectively. On the other hand, when the second carbon is short carbon fibers and/or carbon particles, ion diffusion between graphenes is not hindered unlike the case of using general CNTs.

Here, graphene is a carbon material whose minimum unit is a graphene sheet having a thickness of one carbon atom, and usually constitutes a laminate in which a plurality of graphene sheets are laminated. A graphene sheet is an aggregate or molecule composed of sp2-bonded carbon having a thickness of one carbon atom, and has a honeycomb-like lattice structure that spreads out like a sheet. General graphene usually has a flat sheet-like form, but here, various forms of graphene sheet laminates with disordered layer structures (or disordered interlayer distances) are also included in the graphene category. . Graphene may partially include graphene analogs such as graphene oxide. Hereinafter, graphene is also referred to as a graphene sheet laminate.

The capacitor electrode has, for example, a metal current collector and an electrode layer supported on the current collector, and the first carbon and the second carbon are active materials that adsorb and desorb ions, and the electrode layer included in

(a) The first carbon graphene may have a micro three-dimensional structure (ie, microstructure). By having a three-dimensional structure, overlapping of graphene sheets is remarkably suppressed, and the surface area of graphene can be used more effectively. A plurality of raised portions or a plurality of depressed portions are formed on the main surface of the graphene sheet laminate having a three-dimensional structure. With such a three-dimensional structure, the distance between the graphene sheets is appropriately controlled, and the overlapping of the graphene sheets is effectively reduced.

The average number of stacked graphene sheet laminates in graphene is, for example, 10 layers or less, and may be 5 layers or less. Graphene is more desirable as it approaches the smallest unit graphene sheet (ie, monolayer sheet) having a thickness of one carbon atom. The average number of layers may be the number of layers estimated from the interplanar distance (d002) calculated from the diffraction peak attributed to the 002 plane of the X-ray diffraction profile (for example, the Physical Society of Japan 2015 Autumn Meeting Summary Collection p1014). Alternatively, an estimated value obtained from an electron microscope (SEM or the like) photograph of graphene may be used. For example, the number of stacked graphene sheets can be estimated from the scale of the SEM photograph of graphene and the interplanar distance between the 002 planes (hereinafter also referred to as basal planes) of the graphene sheets. For example, arbitrarily select 20 graphene sheet laminates, estimate the number of laminates for each, omit the 5th maximum number and the 5th minimum number, and 10 intermediate graphene sheet laminates. The average value of the numerical values may be taken as the average lamination number.

The interlayer distance (that is, the distance between basal planes) between graphene sheets in graphene may vary randomly. Random variation of interlayer distance means that graphene has low crystallinity. The greater the disorder in the laminated structure of graphene, the more pronounced the change in the interlayer distance.

Graphene may have three-dimensional structures, such as crimped or folded structures. At this time, each graphene sheet laminate itself has a microporous structure. Therefore, diffusion of ions near the surface of graphene becomes better. The presence of a crimped structure or a folded structure can be confirmed by electron microscope (SEM, TEM, etc.) photographs of graphene.

The crimped structure may be, for example, a structure having a plurality of randomly formed fold-like protuberances and depressions. A folded structure is a structure having a folded portion in which one graphene sheet laminate is partially folded multiple times, and is included in the category of a crimped structure. The height of the raised portion or the depth of the recessed portion formed in the folded portion may be greater than the thickness of the carbon portion of the graphene sheet laminate having the structure, and may be at least twice the thickness of the carbon portion. good.

The X-ray diffraction profile of the first carbon usually has a diffraction peak P1 assigned to the 002 plane. The larger the overlap between the graphene sheets and the higher the crystallinity of the graphene, the sharper the diffraction peak P1.

On the other hand, when graphene has a three-dimensional structure, the diffraction peak P1 becomes broad and can be separated into a plurality of peaks. A halo pattern attributed to an amorphous phase may be observed on the higher angle side than the diffraction peak P1 of the X-ray diffraction profile of the first carbon.

The interplanar distance (d002) between the 002 planes of the first carbon calculated from the X-ray diffraction profile may be, for example, 0.338 nm (3.38 Å) or more. d002 is calculated by separating the waveform of the diffraction peak observed in the region near 2θ=26.38°, calculating d002 for each component, and averaging them. The distance (d002) of the 002 plane of the first carbon is preferably 0.340 nm (3.40 Å) or more, more preferably 0.360 nm (3.60 Å) or more, and 0.370 nm (3.70 Å) or more. More preferred.

(b) Second Carbon The second carbon may be short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less.

(i) Short carbon fiber The short carbon fiber may be, for example, vapor-grown carbon fiber, carbon nanotube, carbon nanofiber, or the like. The short carbon fiber may have a hollow space (hollow portion) inside.

The average length of the short carbon fibers may be 10 μm or less, but is preferably 2 μm or less, more preferably 0.1 μm or less, from the viewpoint of increasing ion diffusivity between graphenes. The average length of short carbon fibers can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, select 20 arbitrarily short carbon fibers, measure the length of each, omit the 5th maximum value and the 5th minimum value, and 10 intermediate values should be taken as the average length. In addition, since the short carbon fibers are as short as 10 μm or less, they can be approximated to be substantially linear. Therefore, the length of a short carbon fiber means the length of a straight line connecting both ends of the short carbon fiber.

The average diameter of the short carbon fibers is, for example, 200 nm or less, may be 5 nm or more and 200 nm or less, or may be 10 nm or more and 170 nm or less. The diameter of the short carbon fibers is the maximum length in the direction perpendicular to the longitudinal direction of the short carbon fibers, and the average diameter can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, select 20 arbitrarily short carbon fibers, measure the diameter of each, omit the 5th maximum value and the 5th minimum value, and 10 intermediate values The average value should be taken as the average diameter.

(ii) Carbon Particles The average diameter of the carbon particles may be 0.1 μm or less, but is preferably 0.05 μm or less, more preferably 0.03 μm or less, from the viewpoint of increasing the ion diffusibility between graphenes. The average diameter of carbon particles can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, arbitrarily select 20 carbon particles, measure the maximum diameter of each, omit the 5th largest value and the 5th smallest value, and 10 values in between. The average value may be taken as the average diameter. In addition, when the carbon particles can be separated, the measurement can be performed with a laser diffraction particle size distribution analyzer. In this case, the median diameter of 50% cumulative volume in the volume-based particle size distribution may be taken as the average diameter.

Specific examples of carbon particles include graphite, non-graphitizable carbon, graphitizable carbon, and carbon black. Among them, carbon black is preferable, and for example, acetylene black, ketjen black, thermal black, furnace black, channel black and the like can be used. A plurality of carbon particles (here, primary particles) may be connected to form a chain structure (secondary particles). In this case, the mean diameter is the mean diameter of the primary particles. The length of the chain structure is not particularly limited, but is preferably 2 μm or less, preferably 0.5 μm or less, and more preferably 0.05 μm or less.

(iii) Ratio of first carbon/second carbon The ratio of the first carbon to the total of the first carbon and the second carbon may be 40 to 98% by mass, and may be 80 to 98% by mass. In order to obtain a high-capacity capacitor electrode, it is desirable that the proportion of graphene having a large surface area is large. On the other hand, if the ratio of the first carbon is too large, the amount of the second carbon interposed between the graphenes is reduced, and the effect of suppressing the overlapping of the graphene sheets is reduced. If the ratio of the first carbon is within the above range, the overlapping of the graphene sheets is significantly suppressed, so the capacity of the capacitor electrode can be efficiently increased.

(c) Binder The capacitor electrode may contain a binder. The binder is used to bind the first carbons together, bind the second carbons together, or bond the first carbons and the second carbons together when molding a mixture of the first carbons and the second carbons into a sheet-like or film-like electrode layer. It has a role of assisting the bonding with 2 carbons. Further, the binder has a role of assisting the bonding between the electrode layer and the current collector.

Binders include, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine resins such as vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), carboxymethyl cellulose (CMC), poly Water-soluble resins such as ethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyvinyl acetate etc. can be used.

(d) Third Component The electrode layer may contain other active material such as activated carbon in addition to the first carbon and the second carbon. Also, the present invention does not exclude the case where the electrode layer contains CNTs having an average length of more than 10 μm, and the electrode layer may contain a small amount of CNTs.

(e) Current collector A metal foil, a metal porous body, or the like can be used as the current collector. Aluminum, copper, nickel, iron, stainless steel, platinum, and the like can be used as the material of the current collector. Alloys containing these metals as main components may also be used. The metal foil may be a plain foil, but may also be a foil roughened by etching or the like, a plasma-treated foil, or the like. A metal porous body has, for example, a three-dimensional network structure.

The mass per unit area of the porous metal body may be, for example, 500 g/m ² or less, or 150 g/m ² or less. The porosity of the metal porous body may be, for example, 80% to 98% by volume, and may be 90% to 98% by volume.

The average pore diameter of the pores of the metal porous body may be, for example, 50 μm or more and 1000 μm or less, may be 400 μm or more and 900 μm or less, or may be 450 μm or more and 850 μm or less.

Next, an example of a method for manufacturing capacitor electrodes will be described.
(i) Dispersion Preparation Step First, an aqueous dispersion containing the first carbon raw material and the second carbon is prepared. The first carbon material is a precursor of the first carbon, and graphene oxide is used here. The second carbon is short carbon fibers with an average length of 10 μm or less and/or carbon particles with an average diameter of 0.1 μm or less.

The aqueous dispersion may contain a dispersing agent such as carboxymethyl cellulose (CMC) in addition to the first carbon raw material, the second carbon and water.

Graphene oxide is a graphene analogue having an oxygen-containing functional group, and is, for example, a material exfoliated from graphite in a single layer or multiple layers through oxidation of graphite. The oxygen-containing functional group is a hydrophilic group such as a hydroxyl group, a carbonyl group, a carboxyl group, etc., and has water dispersibility.

Oxidation of graphite can be performed, for example, in water using an oxidizing agent. Sulfuric acid, potassium permanganate, chromic acid, sodium dichromate, sodium nitrate, peroxides, persulfates, organic peracids and the like can be used as the oxidizing agent. A water-soluble solvent may be added to the water. Examples of water-soluble solvents include alcohols, ketones such as acetone, and ethers such as dioxane and tetrahydrofuran. An oxidation reaction in water produces an aqueous dispersion of graphene oxide. By adding the second carbon to the aqueous dispersion of graphene oxide, an aqueous dispersion containing the first carbon raw material and the second carbon is obtained.

The degree of oxidation (oxygen content) of graphene oxide may be, for example, 10 to 60% by mass, 20 to 50% by mass, or 30 to 50% by mass. The degree of oxidation of graphene oxide can be measured, for example, by X-ray photoelectron spectroscopy (XPS). The masses of carbon (C) and oxygen (O) contained in graphene oxide may be measured by XPS, and the mass ratio of oxygen to the total mass of carbon and oxygen may be calculated.

(ii) Reduction Step Next, graphene oxide is reduced in an aqueous dispersion containing graphene oxide (first carbon source material) and second carbon, that is, in the presence of second carbon. The reduction method is not particularly limited, but includes, for example, hydrothermal treatment. For example, a gel-like product may be produced by encapsulating the aqueous dispersion in an autoclave and subjecting it to hydrothermal treatment. The temperature of the hydrothermal treatment may be, for example, 150° C. or higher, preferably 170° C. or higher and 200° C. or lower.

The hydrothermal treatment can produce a crosslinked structure between the first carbon and the second carbon. For example, the first carbon and the second carbon are crosslinked via a functional group such as an ether bond group (--O--). According to such a hydrothermal treatment, a gel-like product containing graphene that is composited with the second carbon and has a three-dimensional structure is obtained.

The gelled product may be contacted with a reducing agent in order to further advance the reduction. Examples of reducing agents include metal hydrides, borohydrides, boranes, hydrazines or hydrazides, ascorbic acids, thioglycolic acids, cysteines, sulfites, thiosulfates, and dithionites. For example, the gelled product may be immersed in an aqueous solution containing a water-soluble reducing agent such as sodium ascorbate. The temperature of the aqueous solution may be, for example, 20 to 110°C, may be 40 to 100°C, or may be 50 to 100°C. The amount of the reducing agent to be used may be appropriately adjusted according to the type of reducing agent, the degree of oxidation of graphene oxide, the amount of gelled product, and the like. The degree of oxidation of graphene after reduction may be, for example, 40% by mass or less, or may be 20% by mass or less.

(iii) Freeze-drying step After that, the gel-like product is preferably lyophilized (freeze-dried). By freeze-drying, a dry gel (xerogel) in which the three-dimensional structure of graphene is highly maintained can be obtained. Freeze-drying may be performed, for example, at -50°C to 0°C, preferably -50°C to -20°C, under reduced pressure of 100 Pa or less, preferably 1 Pa or less.

A xerogel is a composite of graphene and secondary carbon with a three-dimensional structure. The composite contains graphene having a three-dimensional structure laminated via the second carbon. The composite is used as an active material for capacitor electrodes that exhibit high capacity.

(iv) Electrode formation step Next, the composite of the first carbon and the second carbon is dispersed in a dispersion medium such as water together with a binder to prepare a slurry. At this time, if the second carbon intervenes between the graphenes, rearrangement of the graphene sheets is suppressed even in the slurry, and further formation of overlap between the graphene sheets is suppressed. In addition, in the composite obtained through hydrothermal treatment, the first carbon and the second carbon are usually crosslinked via functional groups, and the degree of freedom of movement of graphene is restricted. Therefore, the three-dimensional structure is easily maintained even in the slurry.

The resulting slurry is applied to a current collector and the coating film is dried to form an electrode layer carried on the current collector, thereby obtaining a capacitor electrode. After that, the electrode layer may be rolled.

Next, an example of a capacitor provided with the capacitor electrode will be described. The capacitor electrode can be applied as an electrode for, for example, an electric double layer capacitor, a lithium ion capacitor, or the like.

FIG. 1 is a partially cutaway perspective view of an electric double layer capacitor 10. FIG.
The illustrated electric double layer capacitor 10 includes a wound capacitor element 1 . The capacitor element 1 is configured by winding a sheet-like first electrode 2 and a sheet-like second electrode 3 with a separator 4 interposed therebetween. The first electrode 2 and the second electrode 3 each have a first current collector and a second current collector made of metal, and a first electrode layer and a second electrode layer supported on the surface thereof, and adsorb ions. And the capacity is expressed by desorption. Aluminum foil, for example, is used for the first and second current collectors. The surface of the current collector may be roughened by a technique such as etching. For the separator 4, for example, a nonwoven fabric containing cellulose as a main component is used. Lead wires 5a and 5b are connected to the first electrode 2 and the second electrode 3, respectively, as lead members. Capacitor element 1 is housed in a cylindrical exterior case 6 together with an electrolytic solution (not shown). The material of the exterior case 6 may be any metal such as aluminum, stainless steel, copper, iron, brass, or the like. The opening of the exterior case 6 is sealed with a sealing member 7 . The lead wires 5 a and 5 b are led out to the outside so as to pass through the sealing member 7 . A rubber material such as butyl rubber, for example, is used for the sealing member 7 .

The electrode layer contains an active material as an essential component, and may contain a binder, a conductive aid, and the like as optional components. The active material comprises a first carbon and a second carbon having the characteristics already described. The electrode layer is formed by, for example, applying a slurry obtained by kneading an active material, a binder (e.g., carboxymethylcellulose (CMC)) and the like with water using a kneader on the surface of the current collector, and drying the coating film. , obtained by rolling.

The electrolytic solution may be a mixture of a solvent and an ionic substance (eg, organic salt) dissolved in the solvent. The solvent may be a non-aqueous solvent or an ionic liquid. The concentration of the ionic substance in the electrolytic solution may be, for example, 0.5 to 2.0 mol/L.

As the non-aqueous solvent, a high boiling point solvent is preferred. For example, lactones such as γ-butyrolactone, carbonates such as propylene carbonate, polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane, N-methylacetamide, N,N-dimethylformamide, N- Amides such as methyl-2-pyrrolidone, esters such as methyl acetate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde can be used.

An organic salt is a salt in which at least one of the anion and cation contains an organic substance. Examples of organic salts whose cations include organic substances include quaternary ammonium salts. Organic salts in which the anion (or both ions) contain an organic substance include, for example, trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, phthalate acid mono 1,3-dimethyl-2-ethylimidazolinium;

From the viewpoint of improving withstand voltage characteristics, the anion preferably contains a fluorine atom, and for example, BF ₄ ^- and/or PF ₆ ^- are used. Preferred organic salts specifically include tetraalkylammonium salts such as ethyltrimethylammonium tetrafluoroborate.

In the above embodiments, a wound capacitor has been described, but the scope of application of the present invention is not limited to the above, and it can also be applied to capacitors of other structures, such as laminated or coin-shaped capacitors.

EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited to the examples.

<<Example 1>>
In this example, a wound electric double layer capacitor (Φ18 mm×L (length) 70 mm) with a rated voltage of 2.8 V was produced. A specific method for manufacturing the electric double layer capacitor will be described below.

(i) Preparation of active material An aqueous dispersion containing 0.35% by mass of graphene oxide as the first carbon raw material was added to carbon black as the second carbon (acetylene black manufactured by Denka Co., Ltd. (average primary particle diameter: 35 nm). )) is added and mixed with a thin film swirling high-speed mixer (Filmix (registered trademark)) manufactured by Primix Co., Ltd., and the total content of the first carbon raw material and the second carbon is 0.39% by mass. A dispersion was prepared.

Next, the aqueous dispersion was hydrothermally treated at 180° C. for 1 hour to obtain a gel-like product. Subsequently, the gel-like product was immersed in an aqueous sodium ascorbate solution (sodium ascorbate concentration: 1.0 mol/L) as a reducing agent, heated to 100° C. and held for 2 hours to sufficiently reduce graphene oxide. Thereafter, the gel-like product was lyophilized (freeze-dried) at −20° C. under a reduced pressure of 100 Pa to obtain a xerogel.

Next, xerogel (that is, a composite of the first carbon and the second carbon) was dispersed in water together with CMC as a binder to prepare a slurry. The amount of CMC used was 10 parts by mass per 100 parts by mass of xerogel. The obtained slurry was applied to a current collector made of Al foil having a thickness of 30 μm, and the coating film was vacuum-dried at 110° C. and rolled to form an electrode layer, thereby obtaining a capacitor electrode.

A pair of electrodes are prepared, lead wires are connected to each of them, and a capacitor element is formed by winding them with a cellulose non-woven fabric separator interposed therebetween. An electric double layer capacitor A1 was completed. As the electrolytic solution, a solution obtained by dissolving ethyldimethylimidazolium tetrafluoroborate in propylene carbonate, which is a non-aqueous solvent, at a concentration of 1.0 mol/L was used. After that, an aging treatment was performed at 60° C. for 16 hours while applying a rated voltage.

[evaluation]
FIG. 2A shows a TEM photograph of the xerogel used for slurry preparation in this example. FIG. 2B is an enlarged TEM photograph of a portion of FIG. 2A. From these photographs, it can be confirmed that chain-like links of primary particles of carbon black are interposed between the layers of a plurality of graphene sheet laminates.

The TEM image shows a crimped or folded structure with a plurality of randomly formed fold-like protuberances and depressions. The height of the raised portion or the depth of the recessed portion formed in the folded portion is sufficiently larger than the thickness of the carbon portion, and is at least twice the thickness of the carbon portion.

In addition, when the xerogel was subjected to X-ray diffraction measurement, a broad halo pattern attributed to the amorphous phase was observed on the higher angle side than the diffraction peak P1 attributed to the 002 plane, indicating the presence of a crimped structure or a folded structure. was done. When the obtained X-ray diffraction profile was analyzed to obtain d002 of graphene, it was confirmed to be about 0.34 nm or more.

Next, the capacitance of the electric double layer capacitor A1 was determined at 25°C and -30°C. Also, the ratio of −30° C. capacitance/25° C. capacitance (C(−30/20)) was obtained. Since ion diffusion is rate-determining at low temperatures, it can be said that the larger the C(-30/20) ratio, the lower the resistance to ion diffusion.

<<Comparative example 1>>
A xerogel was prepared in the same manner as in Example 1 except that acetylene black as the second carbon was not used, and an electric double layer capacitor B1 was produced using it and evaluated in the same manner.

<<Comparative Example 2>>
A xerogel was prepared in the same manner as in Example 1 except that acetylene black, which is the second carbon, was not used, and 10 parts by mass of acetylene black was added to the slurry per 100 parts by mass of the xerogel. An electric double layer capacitor B2 was produced in the same manner and evaluated in the same manner.

<<Comparative Example 3>>
A slurry containing acetylene black was prepared in the same manner as in Comparative Example 2 except that highly crystalline graphene was used instead of xerogel, and an electric double layer capacitor B3 was produced in the same manner as in Example 1 and evaluated in the same manner. FIG. 3 shows an electron microscope (SEM) photograph of the highly crystalline graphene according to this comparative example.

Table 1 shows the evaluation results of the above examples and comparative examples.

Table 1 shows that the capacitance of capacitor A1 is significantly higher than those of B1 to B3, and that capacitor A1 is a low-resistance capacitor with excellent ion diffusibility even at low temperatures. Note that the capacitances of the capacitors B1 and B2 are significantly lower than that of the capacitor A1, and are almost the same. From this, even if xerogel and acetylene black are mixed during slurry preparation, it is difficult to form a structure that is superior to ion diffusion in which graphenes are laminated via acetylene black. It can be said that maintaining the original structure is also difficult. On the other hand, in the xerogel obtained by freeze-drying the aqueous dispersion of graphene oxide and secondary carbon (carbon black) after reduction, the graphenes are stacked with acetylene black interposed therebetween, and the three-dimensional structure of graphene is maintained. It is considered that This is probably because the first carbon and the second carbon are crosslinked via chemical bonds such as ether bonds, for example.

According to the present invention, an electric double layer capacitor with high capacity and low resistance even at low temperatures can be obtained.

1: capacitor element, 2: first electrode, 3: second electrode, 4: separator, 5a: first lead wire, 5b: second lead wire, 6: exterior case, 7: sealing member, 10: capacitor

Claims (19)

graphene, which is the first carbon;
a short carbon fiber having an average length of less than 0.1 μm, which is the second carbon;
A capacitor electrode, wherein the graphenes are stacked with the short carbon fibers interposed therebetween. 2. The capacitor electrode according to claim 1, wherein said short carbon fibers are vapor-grown carbon fibers or carbon nanofibers. graphene, which is the first carbon;
and carbon particles having an average diameter of 0.1 μm or less, which is the second carbon,
The electrode for a capacitor, wherein the graphenes are stacked with the carbon particles interposed therebetween. 4. The capacitor electrode according to claim 3, wherein said carbon particles are selected from the group consisting of graphite, non-graphitizable carbon, graphitizable carbon and carbon black. 5. The electrode for a capacitor according to claim 3, wherein said chain-like link of carbon particles is interposed between layers of said graphene laminate. The capacitor electrode according to any one of claims 1 to 5, wherein a ratio of said first carbon to a total of said first carbon and said second carbon is 40 to 98% by mass. 7. The capacitor electrode according to claim 1, having a crosslinked structure between said first carbon and said second carbon. 3. The capacitor electrode according to claim 1, wherein said graphene has a degree of oxidation of 40% by mass or less. 9. The capacitor electrode according to claim 1, wherein said graphene has a three-dimensional structure. The capacitor electrode according to any one of claims 1 to 9, wherein the average number of laminated graphene sheets in the graphene is 10 or less. The capacitor electrode according to any one of claims 1 to 10 , wherein the interlayer distance between graphene sheets in the graphene varies randomly. The capacitor electrode according to any one of claims 1 to 11 , wherein the graphene has a crimped structure or a folded structure. Claims 1 to 12 , wherein the X-ray diffraction profile of the first carbon has a diffraction peak P1 attributed to the 002 plane and a halo pattern attributed to an amorphous phase on a higher angle side than the diffraction peak P1. The capacitor electrode according to any one of . 14. The capacitor electrode according to claim 13 , wherein the interplanar distance between the 002 planes of the first carbon calculated from the X-ray diffraction profile is 0.338 nm or more. A capacitor comprising the capacitor electrode according to any one of claims 1 to 14 . preparing an aqueous dispersion containing graphene oxide as the first carbon raw material and the second carbon;
and reducing the graphene oxide in the aqueous dispersion;
The method for producing a capacitor electrode, wherein the second carbon is short carbon fibers having an average length of less than 0.1 μm and/or carbon particles having an average diameter of 0.1 μm or less. 17. The method for producing a capacitor electrode according to claim 16 , wherein the step of reducing the graphene oxide includes obtaining a gel-like product by hydrothermal treatment of heating the aqueous dispersion at a temperature of 150° C. or higher. 18. The method of manufacturing a capacitor electrode according to claim 17 , wherein the step of reducing the graphene oxide further comprises contacting the gelled product with a reducing agent. 19. The method for producing a capacitor electrode according to claim 17 or 18 , further comprising the step of freeze-drying said gel-like product.

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